Various configurations of antenna elements and antenna array configurations have been used for providing wireless communications in systems such as Global System for Mobile Communications (GSM), third generation mobile telecommunications (3G), fourth generation mobile telecommunications (4G), 3GPP Long Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS), wireless fidelity (Wi-Fi), Worldwide Interoperability for Microwave Access (WiMAX), and Wireless Broadband (WiBro). In providing broadband wireless communications, a base station, access point, or other communication node (collectively referred to herein as base stations) often include an array of antenna elements operable to illuminate a service area for providing broadband wireless communications.
An antenna element array as may be utilized by the aforementioned base stations may include a plurality of antenna element columns, each including a plurality of antenna elements, which are coupled to a feed network operable to provide desired antenna patterns (also referred to as “beams”) throughout the service area. In a typical base station antenna system, a plurality of antenna elements (e.g., 4-8) would be disposed with a particular relative spacing (e.g., ¼, ½, or 1 wavelength) to provide an antenna element column. A plurality of antenna element columns (e.g., 3-12) are generally provided, often with a particular relative spacing (e.g., ¼, ½, or 1 wavelength). The signals of the individual elements and/or antenna element columns are combined to constructively and destructively sum and thereby define desired antenna patterns. As can readily be appreciated, such antenna system configurations may comprise a relatively large number of individual antenna elements and/or a complex feed network. Accordingly, base station antenna systems are often costly in both material and the labor required to construct them.
Adding further to the complexity and cost of such antenna systems is the use of dual-polarization (e.g., slant left/slant right or horizontal/vertical) at the base station, such as for signal diversity, multiple-input multiple-output (MIMO), etc. For example, individual antenna elements often must themselves be dual-polarized, requiring dual signal feeds and signal isolation. Alternatively, the number of antenna elements must be doubled to provide individual elements for each desired polarization. Both of the foregoing configurations adds to the base station antenna system costs in both material and the labor required to construct them.
The cost and complexity of the individual antenna elements themselves is not trivial. For example, many current base station antenna system configurations utilize dipole antenna elements such as shown in FIG. 1A. Such dipole antenna elements are a three-dimensional metal structure comprising a pair of metal aerials (e.g., aerials 101a and 101b) physically coupled to a signal feed (e.g., feed 110) which may comprise a balun or other relatively complicated circuitry. Thus, such dipole antenna elements are relatively complicated and labor intensive to manufacture. Where dual-polarization is desired, two such individual dipole elements must be provided, each having a respective polarization, as shown in FIG. 1B (e.g., slant left dipole element 101 and slant right dipole element 102). Such a dual-polarization configuration substantially increases the complexity and cost of the antenna system.
A more recently developed antenna element configuration which is often less costly to manufacture is the patch antenna as shown in FIG. 2A. Such patch antenna elements comprise a conductive patch (e.g., patch 201), disposed in association with a corresponding a ground plane (e.g., ground plane 220), in communication with a signal feed. For example, the signal feed may comprise a coaxial feed wherein a feed pin physically couples the feed network to the patch antenna element as shown in FIG. 2B (e.g., feed pin 211b passing through ground plane 220 without making electrical contact and physically connected, such as by soldering, to patch 201). Such a configuration is relatively expensive and/or complicated to manufacture (e.g., labor intensive to make due to soldering or similar techniques required for the electrical connection). Moreover, the coaxial feed patch antenna element configuration has generally not been found to have good bandwidth performance characteristics.
Accordingly, alternative signal feed configurations for patch antenna elements have been developed. One such signal feed configuration is a L-probe feed wherein a “L” shaped feed pin couples the feed network to the patch antenna element via a dielectric gap as shown in FIG. 2C (e.g., L-probe 211c passing through ground plane 220 without making electrical contact and disposed beneath patch 201 to communicate radio frequency (RF) signals there between). This configuration has been found to have improved bandwidth performance characteristics as compared to the aforementioned coaxial feed configuration. However, the L-probe configuration continues to be relatively expensive and/or complicated to manufacture (e.g., labor intensive to position the L-probe and to provide support structure to retain the proper positioning).
Another alternative signal feed configuration used for patch antenna elements is the microstrip slot feed wherein a microstrip line couples the feed network to the patch antenna element via dielectric coupling through a slot as shown in FIG. 2D (e.g., microstrip line 211d disposed beneath ground plane 220 and communicating RF signals between patch 201 via slot 221d disposed in ground plane 220). Such a configuration is relatively simple to construct using a multilayer printed circuit board providing the proper matching (e.g., dielectric properties) between layers, and thus provides an inexpensive alternative as compared to the aforementioned coaxial feed and L-probe feed patch antenna element configurations. Moreover, as can be seen in FIG. 2C, the microstrip slot feed patch antenna element may be configured to provide dual polarization (e.g., microstrip line 211d disposed beneath ground plane 220 and communicating RF signals between patch 201 via slot 221d disposed in ground plane 220 providing a first polarization and microstrip line 212d disposed beneath ground plane 220 and communicating RF signals between patch 201 via slot 222d disposed in ground plane 220 providing a second polarization).
The foregoing microstrip slot feed patch antenna element configuration is not without disadvantage. For example, microstrip slot feed configurations have been found to present difficulties with respect to impedance matching, often requiring the use of a multiple patch configuration as shown in FIG. 2E (e.g., patch 201 and patch 201e). Although providing improved impedance matching, the use of such dual patch configurations typically results in antenna pattern distortion at various frequencies (i.e., wideband operation is affected). Additionally, although providing for dual polarization, the asymmetry of the signal feeds results in undesired antenna pattern distortion (e.g., beams formed using an array of the microstrip slot feed antenna elements experience a shift in direction, or tilt, resulting from the asymmetric microstrip slot feed configuration). Moreover, the signal isolation provided between the two microstrip slot feeds by microstrip slot feed patch antenna element configurations is on the order of 20 dB, which in many instances is less than necessary or otherwise desired in providing satisfactory system performance.
Yet another alternative signal feed configuration used for patch antenna elements is the printed highly decoupled input port feed patch antenna element configuration shown in FIGS. 2F and 2G. In the configuration of FIGS. 2F and 2G, the feed network built by the microstrip lines couple the RF signals to the patch antenna elements via dielectric coupling through slots (e.g., microstrip lines 211f and 212f disposed beneath ground plane 220 and communicating RF signals between patches 201 and 201f via slots 221f and 222f disposed in ground plane 220). Microstrip line 212f associated with slots 222f couple one of the channel's signal and microstrip line 211f associated with slot 221f couples the other channel's signal, wherein the ends of microstrip line 212f provide coupling of signals to corresponding ones of slots 221f of substantially equal amplitude and phase with respect to each other. Although providing for dual polarization, the impedance matching difficulties associated with this printed highly decoupled input port feed configuration necessitates the use of a second patch (e.g., patch 201f). Moreover, this printed highly decoupled input port feed configuration results in distorted antenna patterns as various frequencies. Accordingly, the printed highly decoupled input port feed patch antenna element configuration is complicated and relatively costly to manufacture (e.g., two patches) while continuing to suffer from some of the antenna pattern distortion problems of the microstrip slot feed patch antenna element configuration. Also, as the signal level on the slots are fully coupled to the patches, the signal level of coupling through the slots cannot be controlled and creates difficulties with respect to impedance matching.